The field of invention relates to direct access data storage, generally. More specifically, the invention relates to compensating for the effect of image current within an AP Pinned magnetic heads.
Hardware systems often include memory storage devices having media on which data can be written to and read from. A direct access storage device (DASD or disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form. Magnetic heads, when writing data, record concentric, radially spaced information tracks on the rotating disks. Magnetic heads also typically include read sensors that read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, the defining structure of MR heads, can read stored data at higher linear densities than thin film heads. A MR head detects the magnetic field(s) through the change in resistance of its MR sensor. The resistance of the MR sensor changes as a function of the direction of the magnetic flux that emanates from the rotating disk.
One type of MR sensor, referred to as a giant magnetoresistive (GMR) effect sensor, takes advantage of the GMR effect. In GMR sensors, the resistance of the MR sensor varies with direction of flux from the rotating disk and as a function of the spin dependent transmission of conducting electrons between magnetic layers separated by a non-magnetic layer (commonly referred to as a spacer) and the accompanying spin dependent scattering within the magnetic layers that takes place at the interface of the magnetic and non-magnetic layers.
GMR sensors using two layers of magnetic material separated by a layer of GMR promoting non-magnetic material are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the magnetic layers, referred to as the pinned layer, has its magnetization direction xe2x80x9cpinnedxe2x80x9d via the influence of exchange coupling with an antiferromagnetic layer. Due to the relatively high internal anisotropy field associated with the pinned layer, the magnetization direction of the pinned layer typically does not rotate from the flux lines that emanate from the rotating disk. The magnetization direction of the other magnetic layer (commonly referred to as a free layer), however, is free to rotate with respect to the flux lines that emanate from the rotating disk.
FIG. 1 shows a prior art SV sensor structure 100 where the pinned layer is implemented as a structure 120 having two ferromagnetic films 121, 122 (also referred to as MP2 and MP1 layers, respectively) separated by a conductive film 123 (such as ruthenium Ru) that provides antiparallel coupling of the two ferromagnetic films 121, 122. Sensor structures such as that 100 shown in FIG. 1 are referred to as AP sensors in light of the antiparallel magnetic relationship between films 121, 122. Similarly, structure 120 may also be referred to as an AP layer 120.
FIG. 1 shows an AP sensor 100 comprising a seed layer 102 formed upon a gap layer 101. The seed layer 102 helps properly form the microstructure of the antiferromagnetic layer 105. Over seed layer 102 is an antiferromagnetic (AFM) 105 layer used to pin the magnetization direction of the MP2 layer 121. MP1 layer 122 is separated from free layer 103 by spacer layer 104. Note that free magnetic layer 103 may be a multilayer structure having two or more magnetic layers.
A problem with structures such as or similar to that shown in FIG. 1 is the net bias exerted on the free layer 103 by the other layers and/or currents associated with the sensor 100.
An apparatus is described comprising a free layer and a spacer layer. The spacer layer is between a first magnetic layer and the free layer where the spacer and first magnetic layers are tailored to produce a coupling bias on the free layer. A conductive layer is between a second magnetic layer and the first magnetic layer. The first and second magnetic layers are magnetized antiparallel with respect to each other. The first and second magnetic layers and the spacer and conductive layers are tailored to produce a pole density bias on the free layer. The apparatus also has a pair of shields. The free layer is located at a position between the shields such that an image bias and a sensor current bias, in summation with the coupling bias and the pole density bias, produce negligible bias on the magnetization direction of the free layer.